Access to renewable energy on the seafloor is limited due to the lack of sunlight, high water flows, thermal gradients, and other traditional avenues of renewable energy extraction. Long term intelligence, surveillance, and reconnaissance (ISR) systems are required to be placed on or under the seafloor to provide information for operational, security, environmental, resource management, communications and other applications. Many of these systems are buried into the seafloor to operate properly or to avoid being fouled by fishing gear and anchors. In addition, these systems often have a short lifetime and need to be repeatedly deployed which leads to extremely high cost of operation.
One such system is a Linear Array BMFC (LA-BMFC), which utilizes the physical structure of an existing buried underwater cable or array to form the sediment fuel cell electrode. Thus rather than engineering and deploying a completely separate energy system to power the seafloor system, the BMFC is built as part of the linear array to form a single integrated unit, and the fuel cell system is deployed with the array just as the array would normally be deployed. In a typical linear array seafloor sensor system, sensors are connected by and separated by lengths of cable that provide power and telemetry for the sensors. The number of sensors and the length of cables vary by application. In the LA-BMFC, these lengths of cable are jacketed with carbon fabric which serve as the anodes for the fuel cell. At various lengths along the cable, small electronics modules connect to cathodes that protrude slightly into the surface water and harvest energy which is then transferred directly onto the linear array power cables. The cathodes for these systems incorporate a buoyant core so that as the system is deployed they stay clear of the seafloor while the remaining portions of the array are fully buried. The approach is applicable to a broad range of configurations and applications.
Advances in BMFC system design have increased feasibility for its use in ocean monitoring, and have been used for powering underwater sensors and communications devices on the seafloor over extended periods of time. However most of these applications have been for demonstration purposes only and integration with operational underwater systems such as a linear array is still an ongoing challenge.